Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole with a small surface area at an air bearing surface (ABS) and a flux return pole (opposing pole) which is magnetically coupled to the main pole and has a large surface area at the ABS. Critical dimensions of the main pole include a neck height and a pole width in a pole tip adjacent to the ABS. Magnetic flux generated in the main pole layer passes through the pole tip into a magnetic media and then back to the write head by entering the flux return pole.
A conventional PMR write head 1 is depicted in FIG. 1. The main pole layer 3 is formed on a substrate 2 that may be an Al2O3 insulation layer which separates the write head from a read head (not shown) in a separated read/write head. The main pole layer 3 is generally made of a material with a high saturation magnetic flux density (Bs) that terminates in a pole tip also referred to as a write pole 3a at an ABS which is the plane 11-11. There is a first insulation layer 4 on the main pole layer 3 and a second insulation layer 5 on the first insulation layer along the ABS. A coil layer 7 is formed on the first insulation layer 4 and is coplanar with the second insulation layer 5. Coils within the coil layer 7 are insulated by a third insulation layer 8 that may be a photoresist. The third insulation layer 8 and coils formed therein extend from the second insulation layer 5 to a connection region 6 also known as a back gap region that magnetically couples the main pole layer 3 to a flux return pole layer 10. Overlying the coil layer 7 is a fourth insulation layer 9 that separates the coils from the flux return pole.
Referring to FIG. 2, a cross-sectional view of the pole tip 3a from the plane 11-11 is shown. During a recording operation, the pole tip 3a and write head 1 move over a magnetic recording track (not shown) in the z direction. The pole tip 3a usually has an inverted trapezoid shape with sloped sides 21, a top surface 22 that has a pole width (track width) w1 and a bottom surface 20 which has a smaller width than the track width. Each side 21 forms an angle β with the bottom surface. The track width is typically determined by an ion milling process that removes excess material from the edges of the main pole layer. However, a subsequent chemical mechanical polish (CMP) process that planarizes the main pole layer 3 is difficult to control and a large variation in the resulting main pole layer thickness may occur. For example, one write head may have a pole tip thickness t1 and track width w1 following the CMP step. On the other hand, a second write head may have a pole tip thickness t2 and track width w2 which are smaller than t1 and w1, respectively, because of a prolonged CMP process time that forms a top surface 22c. The thickness difference (t1−t2) caused by CMP process variation will have an adverse impact on device performance since track width and magnetic flux density delivered by the main pole will vary from one write head to the next. Therefore, a method is needed that can produce a write head which has a more consistent pole width dimension that is not influenced by CMP process variations.
Referring to FIG. 3, another concern with a conventional PMR write head during a recording operation is that the pole tip 3a tends to become skewed at an angle α relative to the recording direction z and the magnitude of α can vary depending on the location of the pole tip on the circular magnetic recording media. In some cases where the skew angle α is large or where the undercut angle β is significant, undesirable writing can occur on a track adjacent to the intended recording track.
In U.S. Pat. No. 6,504,675, the slope angle of the pole sides is allowed to be greater than the maximum skew angle in order to suppress the skew effect. Alternatively, the trailing write pole is comprised of two parts in which a wide trapezoidal section is formed on a narrow rectangular section that is the leading edge.
A main pole layer with an inverted trapezoidal pole tip is embedded in an inorganic insulation layer in U.S. Pat. No. 6,710,973. A trailing edge, a leading edge, or both lateral edges of the main pole may be tapered in a smooth linear or curved fashion.
In U.S. Pat. No. 6,510,024, an upper magnetic pole is trimmed by an ion milling method in which the incident angle of ion particles is controlled to within a range of 65 to 85 degrees. The upper magnetic pole has a trapezoidal shape in which a bottom surface nearer an adjoining read head has a greater width than a top surface.
A method for forming a pole tip width less than 1 micron is described in U.S. Pat. No. 5,649,351 in which a photoresist layer that is 5 to 10 microns thick is used as an ion milling mask to define a rectangular pole tip in a planar write head. The resulting thin film magnetic write head is disclosed in U.S. Pat. No. 5,452,164.